It is merely the process we all use to find out anything. You observe a thing and test it by running it through a couple of filters.
In this case, I watched the insect at its work. Sucking sap. It's true that I didn't show that - I've said more than once that I am still learning my camera. Usually I pick the best shot I manage.
However, the insect reminded me a lot of the bronze stinkbugs that are local pests on citrus trees. Seen below in a huddle. Not sure why they do that. It's different from the pair-mating behaviour.
|Bronc=ze Stinkbugs in Huddle|
Both these insects have that stinkbug shape, feelers, six legs, smooth back.
The Brisbane Wildlife Guide describes seven stinkbugs but not the one in question.
Brisbane Insects Site has dozens of stinkbugs, of many wonderful colours and patterns. Check it out. It's well worth it.
Though I haven't found mine there yet, there are enough other stinkbugs pictured there with one or other similarity to the bug I found, that I am convinced.